(EP2330699)The present invention aims at providing a two-dimensional photonic crystal laser capable of generating symmetrical spots of laser light. The two-dimensional photonic crystal laser includes a two-dimensional photonic crystal 15 made of a plate-shaped member 151 provided with a periodic arrangement of many identically-shaped modified refractive index areas (or holes) 152A through 152D having a refractive index different from that of the plate-shaped member 151; and an active layer provided on one side of the two-dimensional photonic crystal, wherein: the modified refractive index areas are arranged at lattice points of a lattice with a same period at least in two directions; a shape of each the modified refractive index area is such that a feedback strength is different with respect to directions of two primitive lattice vectors of the lattice; the two-dimensional photonic crystal has a periodic structure of a supercell 154, as a unit, which contains a plurality of lattice points; and the sum of the feedback strengths by all modified refractive index areas 152A through 152D in the supercell 154 is identical in each direction of the two primitive lattice vectors.

特許請求の範囲（英語）

[claim1]1. A two-dimensional photonic crystal laser (10), including: a two-dimensional photonic crystal (15) made of a plate-shaped member (151) provided with a periodic arrangement of many identically-shaped modified refractive index areas (152) having a refractive index different from that of the plate-shaped member; and an active layer (13) provided on one side of the two-dimensional photonic crystal, wherein: the modified refractive index areas are arranged at lattice points of a lattice with a same period (a) at least in two directions; a shape of each modified refractive index area is such that a feedback strength is different with respect to directions of two primitive reciprocal lattice vectors of the lattice; the feedback strength being defined by a following formula: (Equation image 5 not included in text) where, S represents an area of a unit cell of the lattice, epsilon (r) represents a permittivity distribution in the unit cell, G 2 represents a reciprocal lattice vector representing a second-order Bragg diffraction, j represents an imaginary unit, and an integral sign Intg S signifies performing an area integration within the unit cell; the two-dimensional photonic crystal has a periodic structure of a supercell (154), as a unit, which contains a plurality of lattice points; and a sum of the feedback strengths by all modified refractive index areas in the supercell is identical in each direction of the two primitive reciprocal lattice vectors, characterised in that the period (a) of the lattice is equal to a wavelength of light in the two-dimensional photonic crystal, wherein the light is generated within the active layer.[claim2]2. The two-dimensional photonic crystal laser according to claim 1, wherein the lattice is any one of a square lattice, a triangular lattice, and an oblique lattice in which the two primitive reciprocal lattice vectors have a same magnitude.[claim3]3. The two-dimensional photonic crystal laser according to claim 2, wherein the lattice is a square lattice, and each of the modified refractive index areas is asymmetrical with respect to an axis at 45 degrees to the two directions in which the modified refractive index areas are arranged with the same period.[claim4]4. The two-dimensional photonic crystal laser according to claim 3, wherein: each of the supercells is composed of four lattice points as a unit, with two lattice points in a vertical direction and two lattice points in a horizontal direction; and in each of the supercells, with respect to a direction of one modified refractive index area, directions of other three modified refractive index areas are at 90, 180, and 270 degrees.[claim5]5. The two-dimensional photonic crystal laser according to claim 3, wherein: each of the supercells is composed of four lattice points as a unit, two lattice points in a vertical direction and two lattice points in a horizontal direction; and in each of the supercells, with respect to a direction of one modified refractive index area, a direction of one modified refractive index area among other three modified refractive index areas is a same and directions of other two modified refractive index areas are at 90 degrees.[claim6]6. The two-dimensional photonic crystal laser according to claim 2, wherein: the lattice is a triangular lattice; each of the supercells is composed of three adjacent lattice points arranged in an equilateral-triangular form as a unit; and in each of the supercells, with respect to a direction of one modified refractive index area, other two modified refractive index areas are oriented at 120 and 240 degrees, respectively.[claim7]7. The two-dimensional photonic crystal laser according to any one of claims 1 through 6, wherein, in each modified refractive index area, no part of the modified refractive index area lies on a gravity center thereof and on a first half-line extending from the gravity center in a direction within a plane of the two-dimensional photonic crystal, while at least a part of the modified refractive index area lies on a second half-line extending from the gravity center in a direction opposite to the first half-line.[claim8]8. The two-dimensional photonic crystal laser according to claim 7, wherein the modified refractive index area is V-shaped.[claim9]9. The two-dimensional photonic crystal laser according to claim 7, wherein the modified refractive index area is a triangular arrangement of three identically-shaped areas having a refractive index different from that of the body material.